This invention relates to an image forming apparatus which is suitably applied to a tandem type color printer, color copier or a color multifunctional peripheral thereof, having a photoreceptor drum and an intermediate transfer belt, as well as a process correction mode and a correction mode of color misregistration (processing).
In recent years, the tandem type color printer and the color copier as well as the color multifunctional peripheral thereof have been widely used. In this type of color image forming apparatus, in order to suitably maintain color image print quality (color reproductive quality), yellow (Y), magenta (M), cyan (C), and black (BK) which reproduce the red (R), G (green) and B (blue) in the document image are superimposed on the intermediate transfer belt. The color image formed on an intermediate transfer belt is transferred to a predetermined sheet then fixed at a predetermined temperature.
In order to superimpose the colors Y, M, C and BK with good reproductive qualities, positive color misregistration correction in the image forming unit is essential (called correction processing of color misregistration hereinafter).
For correction processing of color misregistration, the color misregistration detection mark (called registration mark hereinafter) for position detection that is formed on the intermediate transfer belt or the conveyance material transfer belt is detected by a color misregistration sensor (called registration sensor hereinafter) such as a reflection type sensor or the like, and the color misregistration amount for the registration marks of the other colors are calculated with respect to the registration mark of the reference color. Feedback is sent to the colors Y, M and C image forming units such that the color misregistration amount is eliminated and the writing timing for the laser light source is corrected to thereby obtain a good quality color image.
On the other hand, in this type of color copier, in power-saving state where the power source plug is plugged into the power outlet, power is supplied to control systems required for minimum operation such as the clock function and the fax delayed receiving function and the like, and a system is adopted in which, for example, power supply to the fixing device in the image forming system which is required for normal operation is stopped and energy is thereby conserved.
At least when the temperature of fixing device in the image forming system is less than a predetermined value, the operation by which the fixing temperature is increased to a predetermined value is the process correction mode, and the process correction mode is set for example at the first power-on when the power supply for the copier is first turned on. A specific example is the case of use in an office, school or the like, when a person who arrives to work in the morning of a particular day and switches on the power source for the color copier for the first time in the morning. In other words, a specific example is the case of the first power-on on that day.
In the color copier, in the case where the process correction mode is set, warming up and process correction processing such as correction processing of color misregistration, image density adjustment and the like are performed. In the correction process of color misregistration, first, the process of writing the registration mark in the image area of the photoreceptor drum is performed. That is to say, correction process of color misregistration is performed before the printing operations related to the image formation job are performed. In the foregoing correction process of color misregistration, after the process of writing the registration mark is performed, the time for the passage of the registration mark is read and the amount of mispositioning of the registration marks of the other colors with respect to the reference registration mark is calculated, and the image formation position is corrected based on the amount of mispositioning. As a result, during regular operation, the colors Y, M, C and BK can be superimposed with good reproductive quality. An image formation job request can be received during these correction operations and at the point when all the correction operations are complete, the image forming operations begins.
In this type of color copier, the power saving mode is often set before the process correction mode is set. In this state, the power supply plug of the copier is connected to a commercial power source, and the power supply to the image forming unit is cut off and power required for minimum operation is supplied to other load circuits such as the clock function, the CPU function, the monitor display function, the communication function (facsimile) and the like. It is to be noted that when a facsimile is being received, if the power saving mode is cancelled, and the device transitions to the normal operation mode. In the normal operation mode, power is also supplied to the fixing device of the image forming system in addition to load circuits other than the control system and the image formation job is performed and then the image formation job is queued.
A color image forming apparatus relating to the foregoing color copier is described in Unexamined Japanese Patent Application Publication No. 2005-91901 (Page 7, FIG. 9). According to this color image forming apparatus, a position detection pattern is detected, and in the case where correction process of color misregistration is performed based on the results of the detection, a non-image part density pattern is formed and the density pattern is detected, and the conditions for creating the position detection pattern at the time of correction process of color misregistration are determined. When the color image forming apparatus is constructed in this manner, the correction process of color misregistration can be performed with a position detection pattern in which the density is adjusted.
It is to be noted that the color image forming apparatus of the prior art has the following problems.
(i). In the process correction mode in which the power switch is turned on for the first time in the morning, an image formation job can be received during the correction process of color misregistration, but the image forming process actually begins at the point when the correction processes are complete. Thus, the users strongly feel that they must wait a long time until image formation actually begins after the power switch is turned on.
(ii). The time required for the correction process of color misregistration is about 1-2 minutes. In the recent fixing devices that use the IH (Induction Heating) heater and the like, the warm-up times has been shortened to under 30 seconds and the fixing temperature is reached in a shorter period compared to conventional types. Despite this, in the copier which carries out the process correction mode and the correction process of color misregistration, there is a problem in that it cannot proceed to a state where copying is permitted (possible) because warming up and correction process of color misregistration is not completed.
(iii). Given the foregoing correction process of color misregistration at first power-on, a method may be considered which employs a structure in which the registration mark (also called mark image hereinafter) is created at a position with sufficient margin for paper offsetting at both sides of the image area and the correction process of color misregistration is done in real time (Density patch image in Unexamined Japanese Patent Application Publication No. 2005-91901).
In this method as well, in the case where the priority ranking for the correction process of color misregistration is ranked high among process correction processing done at first power-on, until all the process correction processing apart from correction process of color misregistration done for the at first power-on complete, as is the case in (ii) above, even if a monochrome image formation job is received, there is a problem in that transition is not possible to a state where copying in the image forming process is permitted (possible).